Curable silicone compositions are used in sealing materials and protective coating materials for optical semiconductor elements in optical semiconductor devices such as light emitting diodes (LED). However, because cured products of curable silicone compositions exhibit high gas permeability, in cases where such cured products are used in high brightness LEDs, which exhibit high light intensity and generate large amounts of heat, problems occur such as discoloration of the sealing material due to corrosive gases and a reduction in brightness due to corrosion of silver plated on the LED substrate.
As a result, Japanese Unexamined Patent Application Publication No. 2012-052045 proposes a curable silicone composition comprising a branched chain organopolysiloxane having a methylphenylvinylsiloxane unit, an organohydrogenpolysiloxane and an addition reaction catalyst as a curable silicone composition that forms a cured product having low gas permeability.
However, Japanese Unexamined Patent Application Publication No, 2012-052045 suggests that the gas permeability of a cured product is reduced by having a molecular structure of an alkenyl group-containing organopolysiloxane in the curable silicone composition, but does not suggest that the gas permeability of a cured product is reduced by having a molecular structure of an organohydrogenpolysiloxane, which is a crosslinking agent.
An object of the present invention is to provide a curable silicone composition that forms a cured product having a high refractive index and a low gas permeability. In addition, another object of the present invention is to provide a cured product having a high refractive index and a low gas permeability and to provide an optical semiconductor device having excellent reliability.